The object of the instant invention is to provide a method for polymerizing in situ and durably fixing selected multivalent metal salts of carboxyl-containing vinyl monomers in and on natural fibers and synthetic fibers so that the metal carboxylate polymer may contribute special performance qualities to the fibrous substrate.
Another object of the invention is to provide a new method for rendering textiles flame resistant and mold inhibiting, for conferring resistance to the development of malador from perspiration in textiles, and for developing unique reversible hydroplastic qualities in textiles.
A further object of this invention is to develop self-sanitizing and biocidal qualities in fibrous substrates.
A still further object of this invention is to develop other fabric properties of commercial value by treatment of fibrous substrates with polymerizable multivalent metal-containing vinyl compounds.
It is known that a variety of water-soluble metal salts may be applied to fibrous substrates constituted of cotton or rayon fibers in order to fire proof these substrates; background is summarized by J. E. Ramsbottom ("The Fireproofing of Fabrics," His Majesty's Stationery Office, 1974). Commonly, the effectiveness of these agents was lost after boiling for one hour in water.
It is also known that a variety of metal salts of mercury and silver are effective antibacterial agents, as is, and when applied to fabrics; compounds of metals other than mercury and silver are of lesser importance as antibacterial agents but are more importent for "hidden" antibacterial action: e.g., aluminum and zinc salts applied as ingredients of cosmetic deodorants control bacterial flora of the skin, thereby preventing microbial decomposition and resulting malodor of perspiration in the axillary area. Background information is summarized by R. S. Mohamed (in Chapt. IX "Antibacterial and Antifungal Finishes" of Chemical Aftertreatment of Textiles, editors, H. Mark, N. S. Wooding, and S. M. Atlas, Wiley-Interscience, New York, 1971, p. 507) and by E. G. Klarmann (in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd edition, Vol. 2, Interscience Publishers, New York, p. 622).
It is further generally known that the application and fixation of chemical agents on and in fibrous substrates increase the stiffness of the products. This stiffness is only little changed by wetting the composition. It is desirable, however, for the preparation of casts, molds, and rigidly shaped products that there be a transition from a flexible state to a rigid state. It is useful that this be accomplished as the wet fibrous substrate (completely flexible and moldable) looses water to reach equilibrium with ambient conditions of humidity and temperature.
It is known that carboxyl-containing vinyl polymers may be applied to fibrous substrates from aqueous solution, emulsion, or dispersion. Such coatings are limited to the surfaces of the fibrous substrates, often accumulating at fiber crossover points. The in-place neutralization of these coatings to convert them to heavy-metl salts occurs slowly and often with loss of some of the carboxyl-containing polymer. Moreover, the predominant deposition of these polymers on the surfaces of the fibrous materials has a detrimental effect on the overall balance of performance properties.
It has now been found that polymers of multivalent metal salts of water-soluble carboxyl-containing vinyl monomers can be deposited, efficiently polymerized in situ, and durably fixed in and on natural and synthetic fibers in compositions ranging from 100% cellulosic or natural fiber to 100% synthetic fiber by a process that involves a water-soluble polyvalent metal salt of a carboxyl-containing vinyl monomer, preferably with a small fraction of a water-soluble di- or polyfunctional vinyl monomer, and a free radical initiator applied from aqueous solution to the fibrous substrate and cured under specific conditions.
In accordance with the present invention, a process is provided for depositing polymer in and on various substrates with effectiveness for imparting flame retardancy, mold inhibition, resistance to the development of malodor from perspiration, and reversible plasticity in transition from the wet to the dry state.
The process is comprised of a treatment of the fibrous structure or textile material with the metal salt of the carboxyl-containing vinyl monomer, the presence or absence of an additional water-soluble monofunctional vinyl monomer, and a di- or polyfunctional vinyl monomer that are curable to network structures and durable finishes, imparting the above-mentioned properties to the fibrous substrates.
It was unexpectedly discovered that the forementioned metal salt vinyl monomers, in contrast to the free acid vinyl monomers can be polymerized to high conversions of monomer to polymer in and on fibrous substrates and that the polymers are durably fixed in and on these substrates. The metal salts of the carboxyl-containing vinyl monomers, together with the comonomers, penetrate well into the void and pore structures of fibers, especially fibers of the cellulosic and protein classes. The network polymeric structures are developed in these regions of the fiber as well as on the surfaces of the fibers; the results are relatively low contribution of the network polymer at low add-ons to the development of stiffness in the fibrous substrate and relatively high durabilities of the polymeric network structure.
It will become apparent in the light of illustrations and examples that the instant process provides a simple means for developing network structures involving metal salts of carboxyl-containing vinyl monomers. These metal salt-containing fibrous substrates have interesting performance qualities, especially reduced flammability of the substrates, increased durability of cellulosic substrates upon exposure to soil and weather, attractive self-sanitizing characterisitics, and unique plasticities. These performance characteristics are not achieved in similiar degree by impregnating a metal base into the pre-deposited carboxyl-containing polymer nor by coating fibrous substrates with heavy-metal neutralized carboxyl-containing polymer materials. The latter become insoluble during initial combination of the heavy-metal base and the carboxyl-containing polymer prior to contact with the fibrous substrate, and in any case, these coatings, once deposited, are limited to the outermost surfaces of the fibers and, because the network structure is limited to ionic crosslinks rather than to the carbon-chain crosslinks as the case in this invention, the polymeric deposits are nondurable.
In order to achieve desired conversions of heavy-metal containing monomers to polymers, desired fixation of polymers to substrates, and desired performance properites in the finished fibrous substrates, it is necessary to conduct the reaction with water-soluble free-radical initiators and to carry out the curing step under controlled conditions such that contacts with air during this stage are not excessive. In general, the curing step may be conducted in complete presence of air when the transfer of the heat to the substrate is achieved through conduction from hot solid surfaces, such as rolls "cans," calender, press, or conventional household iron. Transfer of heat might likewise be conducted without special precuations regarding the presence of air when the heat transfer medium involves steam or vapors, such as those from chlorinated hydrocarbons that are commonly used in textile and drycleaning operations. However, when the transfer of heat is conveyed through the gaseous state, it is desirable that air be diluted with an inert gas such as nitrogen or carbon dioxide or that it be diluted with steam; a direct blast of hot air on the substrate impregnated with the aqueous solution of reagents is undesirable and detrimental to polymerization and fixation. It is not essential that air be completely absent; the extent of dilution that is required is relatively low since the vaporation of water from the reagent solution on the substrate provides a degree of dilution that is sufficient in many cases.
It is desirable in order to achieve the full objective of this invention to include in the reagent formulation small amounts of a water-soluble di-or polyfunctional monomer. The presence of such a monomer in conjunction with a major monomer or monomers has general effects of raising the efficiency of conversion of the monomer to polymer and of improving the durability of the polymer.
The essence of the invention, then, is the discovery that high levels of efficiency of conversion of water-soluble metal salts of carboxyl-containing vinyl monomers to polymers can be realized on fibrous substrates under controlled conditions of cure that are well suited to use in textile mills to obtain modified substrates wherein the reduced combustibility, the biocidal characteristics, the sanitizing properties and the plastic characteristics conferred by the fixed polymers are the basis for valuable performance qualities in fibers, yarns, and textile and paper products.
This invention employs multivalent metal salts of water-soluble carboxyl-containing vinyl monomers. The metal ions involved may be magnesium, calcium, barium, aluminum, titanium, vanadium, chromium, iron, cobalt, nickel, copper, zinc, zirconium, iron, cobalt, nickel, copper, zinc, zirconium, molybdenum, silver, cadmium, beryllium, tungsten, mercury, lead, bismuth, yttrium, and rare earth elements. The water-soluble carboxyl-containing vinyl monomers include acrylic acid, methacrylic acid, and itaconic acid. The concentration of multivalent metal salts of water-soluble carboxyl-containing vinyl monomers range from 1-40 weight percent.
The water-soluble di- or polyfunctional vinyl monomers preferred for the purpose of this invention are methylenebisacrylamide and 1,3,5-triacyloylhexahydro-s-triazine. The concentration of polyfunctional monomers in the solution can vary between 0-3 weight percent.
Monofunctional comonomers are of definite value in this invention to provide facile complexing sites for the metal ion. Preferred comonomers include the following: acrylamide, methyacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, dimethyl-2-hydroxypropylaminemethacrylimide, diacetoneacrylamide, methylolated diacetoneacrylamide, N-vinyl-2-pyrrolidone, hydroxyethylacrylamide, and hydroxyethylmethacrylamide. Other water-soluble acrylic-type monomers may be employed in specific cases; these include hydroxyethyl acrylate and methacrylate, hydroxypropyl acrylate and methacrylate, and dialkylaminoethyl acrylates and methylacrylates. The concentration of monofunctional comonomers ranges from 0-15 weight percent.
Among the catalysts or initiators that are effective and preferred for use in this invention are: ammonium, sodium, and potassium persulfate, hydrogen peroxide, peracetic acid, and t-butylhydroperoxide. The concentration of catalysts in the solution ranges from about 0.03 to about 3.0 weight percent.
A wetting agent, although not essential, is commonly employed to facilitate contact of the aqueous solution of reagents with the surfaces of the fibers in the substrate and to facilitate penetration of the reagents into voids and pores of the fibers. Suitable wetting agents are alkali metal alkylsulfosuccinates and ethylene oxide derivatives of alkylated phenols and high molecular weight alcohols.
The vinyl monomers, the di- or polyfunctional reagent, the initiator, and the wetting agent are dissolved in a suitable amount of water for application to the fiber substrate. The total concentration of monomers in the solution can vary over a wide range, for example between 0.1 and 50%, although the preferred concentrations lie between 1 and 40% by weight.
The reagent solution is applied to the substrate in any suitable manner, but the common and preferred method involves immersion of the fiber substrate in the reagent solution followed by compression of the fiber substrate between rolls to express the excess solution. One or more such sequence of operations is commonly employed. The impregnated fibrous substrates are brought to elevated temperature to activate the initiator and to allow polymerization to occur rapidly and completely. The temperature of cure may range from 75.degree. to 200.degree. C and the periods allowed for initiation and polymerization can range from 120 minutes to approximately 0.5 minutes, the latter time being most appropriate for the highest temperature. Preferred temperatures for cure range from 90.degree. to 160.degree. C with corresponding duration of polymerization of 20 minutes down to one minute.